248 R. \V. HEGXER. 



brushed with a fine camel-hair brush, so as to imitate the crawling movement of 

 small crustaceans, but the valve did not open. We may, therefore, conclude that 

 animals enter merely by forcing their way through the slit-like orifice; their heads 

 serving as a wedge." 



Mrs. Treat (1875) seems to have been the first to study the 

 method of capture employed by the utricularia bladders. Her 

 description, in part, is as follows: 'They (little animals) would 

 sometimes dally about the open entrance (the vestibule) for a 

 short time, but would sooner or later venture in, and easily 

 open or push apart the closed entrance at the other extremity. 

 As soon as the animal was fairly in, the forced entrance closed, 

 making it a secure prisoner." 'I never saw even the smallest 

 animalcule escape after it was once fairly inside the bladder." 



According to Biisgen (1888) animals do not force their way 

 into the bladder between the edge of the valve and the wall of 

 the bladder as supposed by Darwin. They were able to creep 

 about on the outer surface of the valve for considerable periods 

 without being engulfed but suddenly the valve would open and 

 close again and the animals would disappear within. He believed 

 that the mucus on the wall of the bladder where it meets the 

 valve helps to precipitate the prey into the cavity of the bladder 

 and that the mucus and bristles at the mouth of the bladder 

 may stimulate the animal to violent movements which cause 

 the valve to open. The sudden opening of the valve led him 

 to think that he was dealing with a phenomenon of irritability, 

 but he found as did Darwin that stimulation of the bristles with 

 a needle or brush did not cause the opening of the valve. Biisgen 

 almost arrived at the correct method employed by the bladders 

 in capturing animals but apparently did not note the distension 

 of the walls of the bladder and hence missed the essential feature 

 of the process. 



Goebel (1891) agreed with Mrs. Treat and with Darwin that 

 the captured animals force their way into the bladders. Certain 

 of the glandular hairs were supposed by him to be attractive to 

 microorganisms, and other glandular hairs to be so located as 

 to aid the animals to enter the bladder. 



Mueller (1925) in an article entitled 'The Rotifer Group" 

 published two figures showing utricularia bladders. The legends 

 of these figures read in part as follows: (i) "If a rotifer or other 



